Abstract: To enhance the communication stability of urban rail power monitoring systems in complex environments, this study conducts a systematic analysis of the factors influencing communication link reliability based on the Modbus protocol. The analysis covers key dimensions such as network structure, electromagnetic interference, data synchronization, and protocol mechanisms. It proposes a comprehensive improvement strategy combining hardware design, protocol optimization, and redundant architecture, and constructs a test platform for experimental validation. The results show that under a dual-network redundant structure, the error frame rate decreased from 0.83% to 0.28%, the average response time was reduced from 17.2ms to 13.6ms, and the delay jitter was halved. However, when the number of concurrently connected nodes exceeded 24, the frame retransmission rate rapidly increased to 1.63%, resulting in a significant decline in communication performance. In the primary station failure switchover test, the delay in identifying the abnormal frame response trigger mechanism was only 39.1ms, and the switchover completion time was 97.5ms, demonstrating optimal performance. Analysis suggests that integrating fault-tolerance mechanisms with dynamic scheduling strategies can significantly enhance the robustness and real-time response capabilities of Modbus communication systems in urban rail power monitoring.